Real-Time Physics Simulation Forum

Inequality constraints

2007-06-15T08:25:23+00:00

The force is there to hold the box up.

The gravity "pushes" the box in the ground. The contact force counter acts this (actio = reactio). If the box would have a velocity upwards there would be no force.

Statistics: Posted by Dirk Gregorius — Fri Jun 15, 2007 8:25 am

Inequality constraints

2007-06-14T23:07:29+00:00

What Erin is referring to is the fact that the table can only exert an upward/outward force on the box at the point of contact.

In a way this is kind of like the equation "box_bottom_coord >= table_top_coord". Notice the inequality in the equation.

An example of an equality constraint would be wanting the wheel to stay stuck to an axle, e.g. "wheel_center_coord = axle_end_coord".

Gravity is an additional "force" on the box, not a "constraint".

--EK

Statistics: Posted by Eternl Knight — Thu Jun 14, 2007 11:07 pm

Inequality constraints

2007-06-14T21:04:51+00:00

Why do you need a force to hold the box down? Isn't that what gravity does?
Thanks.

Statistics: Posted by daniel_i_l — Thu Jun 14, 2007 9:04 pm

Inequality constraints

2007-06-14T17:07:41+00:00

Imagine you have a box sitting on a table. The table can exert force to hold the box up, but it cannot exert any force to hold the box down. That is the reason for the inequality constraints on the impulses.

Statistics: Posted by Erin Catto — Thu Jun 14, 2007 5:07 pm

Inequality constraints

2007-06-14T15:06:13+00:00

In many tutorials that I've read, such as the slideshow here:
(add periods and slashes)
www gphysics com downloads The collision resolution constraints are modeled as inequalities rather than equalities. But I don't understand, why cant the euqations be written exactly using the impulse equation (the one on chris heckers sight for example) and then solve the system of equations using conventional methods (guass...) instead of LCP?
Thanks.

Statistics: Posted by daniel_i_l — Thu Jun 14, 2007 3:06 pm